1. Field of the Invention
The present general inventive concept relates to an image reading apparatus, and more particularly, to an image reading apparatus in which an image sensor is fixed to a main body of the image reading apparatus and a light scanning carriage that scans a laser onto a document and a light reflection carriage that reflects a light signal to the image sensor are separately moved.
2. Description of the Related Art
Image reading apparatuses scan a laser beam onto a document to read an image printed on a document. Scanners, facsimiles, and multi-function peripherals are examples of the image reading apparatuses.
In order to read the image of the document, a scanning module should move, or the document should be moved. Flat-bed type image reading apparatuses are a type of the image reading apparatus in which the scanning module moves. Sheet-feed type image reading apparatuses are a type of the image reading apparatus in which the document moves. The flat-bed type image reading apparatuses that include an automatic document feeder (ADF) can also perform as the sheet-feed type image reading apparatuses.
The image reading apparatus includes a glass plate on which the document is placed, and the scanning module below the glass plate. The scanning module includes a light scanning carriage scanning light onto the document, an image sensor converting a light signal obtained by reading the document into an electric signal, and a light reflection carriage reflecting the light signal to the image sensor.
The light scanning carriage includes a light source below the glass plate for scanning the light onto the document. For example, the light source can be a halogen lamp having a predetermined length along a main scanning direction of the document, and scans the light along the entire main scanning direction at one time.
The image sensor includes a charge-coupled device (CCD) sensor, a control board controlling the operation of the CCD sensor, and a lens unit focusing light signals onto the CCD sensor.
The light reflection carriage forms an optical path from the light source to the image sensor. The light reflection carriage includes a plurality of mirrors reflecting the light signal obtained by reading the document to the image sensor.
In general, there are two types of the scanning module. One type of the scanning module is an integrated type in which the light scanning carriage, the image sensor, and the light reflection carriage are integrally installed in an outer frame of the scanning module, and the outer frame, the light scanning member, the image sensor, and the light reflection member move together along a sub-scanning direction to read the image of the document. The sub-scanning direction is perpendicular to the main scanning direction.
The second type of scanning module is a separated type, in which the light scanning carriage, the image sensor, and the light reflection carriage are separate. The image sensor is fixed to a main body of the image reading apparatus, and the light scanning carriage and the light reflection carriage move at different speeds from each other along the sub-scanning direction to maintain a total length of the optical path at a constant length. In the separated type scanning module, mass of moving parts can be lower than that in the integrated type scanning module, and thus, the module can move at a high speed. Since the image sensor is fixed to the main body of the image reading apparatus, a resolution can be improved regardless of the size and weight of the sensor. The separate type scanning module is suitable for a high end image reading apparatus that can read large-sized documents at high speed due to a lower mass of inertia of the moving parts.
In an image reading apparatus other than sheet-feed type image reading apparatus, the scanning module should move along the sub-scanning direction to read the image of a document. The image reading apparatus includes a transport module moving the scanning module in the sub-scanning direction. The separated type scanning module includes the transport module that can move the light scanning carriage and the light reflection carriage at different speeds from each other. Therefore, the total length of the optical path from the light source to the image sensor can be maintained constant.
When the size and the weight of the light scanning carriage and the light reflection carriage are increased in order to read a large-sized document, it is hard to control the positions or the velocities of the light scanning carriage and the light reflection carriage. In order to maintain the scanning time at a constant time even when the size of the document increases, the light scanning carriage and the light reflection carriage should move faster. Therefore, a transport module having high accuracy and reliability are required to move the large and heavy light scanning carriage and the light reflection carriage. In addition, when the resolution of the image sensor is high, a precise transport module is required.
The total length of the optical path can be maintained at the constant time when the position of the image sensor, the positions and angles of the mirrors, and a ratio between the velocities of the light scanning carriage and the light reflection carriage are maintained at constant velocities. However, vibrations generated when moving the light scanning carriage and the light reflection carriage, friction, and changes in a driving load may cause a jittering of the light scanning carriage and the light reflection carriage. Thus, the length of the optical path and a reading quality of the image may vary.